The present invention relates to a focusing device for a photographic camera. More particularly, the invention relates to a focus device suitable for use in a photographic camera of a type generally referred to as an auto-process camera.
The so-called auto-process camera employs film units each of which comprises at least a photosensitive sheet exposable to form a latent image of an object to be photographed and transfer sheet on which a positive, viewable image may be produced in a known diffusion-transfer process in which a processing solution normally contained in a breakable pod or pods attached to the film unit, spreads in between the photosensitive sheet and the transfer sheet as the film unit passes through a gap between pressing rolls inside the camera subsequent to exposure of the photosensitive sheet. A photographic print, that is, a developed version of the film unit ejected from the body of the photographic camera, has a relatively large size, for example 80 mm. .times. 70 mm. and is available in a short time after each exposure. Such a camera offers the advantages that it is not necessary for the photographer to proceed to a special establishment for development of film, and also that it is possible to know immediately whether or not a photographic picture has been taken in a desired manner. However, a main disadvantage associated with an auto-process camera is that the camera is comparatively large and bulky, because extra elements for film unit processing and transportation within the body of the camera must be provided therein and also since the camera must accommodate film units each being of a size substantially equal to the size of the final print. Accordingly, it has been a desideratum to reduce the size of the auto-process camera.
A particular aspect of auto-process construction requiring an improvement to be done is a focusing device. The focusing device employed hitherto has generally resulted in increase of the size of the camera. A first problem associated with the focusing device is the location of a viewfinder which forms a part of the focusing device. If, for example, the camera is equipped with a range viewfinder of a type having a range indicator operable in response to forward or rearward movement of the photographic optical system of the camera, there is the inconvenience that the viewfinder is liable to be blocked when a processed film unit is forwarded out of the camera. To avoid this problem it has been known to locate the viewfinder at one side of the body of the camera where it cannot be blocked by film units. However, such a construction has the disadvantage that the camera becomes larger and is somewhat unbalanced, and also that the viewfinder involves a problem of parallax.
To avoid the parallax it has been known to provide an auto-process camera with a through-the-lens viewfinder in combination with a pivotally supported mirror. However, it is known that there are frequently mechanical problems associated with such a mirror, and also since the mirror must have a size comparable with the format of the ultimate photographic print undue amount of space must be made available to accommodate the mirror and permit the reciprocal pivotal motion thereof. This means that the camera becomes even bulkier.